Asked if there’s a possibility that there may be more “Narnia” movies in his future, Ben quipped, “I approached the producers at the after party, after watching very carefully how many glasses of champagne they had. I made sure they had at least three before I broached the question. Caspian is a 70-year-old man, so either they’re going to have to bring Howard Berger (the series’ makeup artist) and his team and I’m going to wake up very early in the morning or they’ll get someone older.’

....

“But, after those aforementioned glasses of champagne, they were talking about maybe doing flashbacks, because in the last chapter of ‘Dawn Treader,’ Caspian and Lilliandil are getting married. There are few potential moments where we could do flashbacks, however.”

Well...they could get an older man who looks VERY much like Ben Barnes. Great for Eustace's not recognizing him and character disconnect as we realize he is old, we are still young. Then have Ben Barnes back when he is young...?

Avy by me, siggy by Dernhelm_of_RohanYou suck a lollipop, and you sing a song. Get it right, Jo!

I don’t think so. While there are some amazing make up artists out there, I don’t think that they have quite perfected the techniques needed to make a 30-year-old look 70. But there is a scene at the end of the next book where the young Caspian returns, so you never know!

Other than the Caspian Young Again Scene, they would need Ben for the flashbacks where they would need to flesh out Caspian's relationship with Lilliandil.

"I'm a beast I am, and a Badger what's more. We don't change. We hold on. I say great good will come of it... And we beasts remember, even if Dwarfs forget, that Narnia was never right except when a son of Adam was King." -Trufflehunter